A wide variety of medical procedures involve the use of a catheter. Typically, the catheter is of a special construction adapted particularly to perform the specific procedure. A typical catheter is in the form of an elongate flexible member, usually tubular, and is adapted to be passed through body passages and lumens to reach the intended site of treatment. The distal end of the catheter, which is disposed within the patient, may carry various devices or elements, among the more common of which is an inflatable balloon. The shape, material and characteristics of the balloon will vary depending on the particular procedure that the balloon is intended to perform. For example, such catheters are used in cardiovascular procedures, such as in angioplasty.
In angioplasty, the object is to widen the passageway through an obstructed or narrowed portion of an artery by inserting the balloon of a balloon dilatation catheter into the obstruction and then inflating the balloon under high pressure to forcibly dilate the obstruction. The angioplasty catheter includes an elongate flexible shaft having a dilatation balloon mounted to the distal end of the shaft. In one type of balloon angioplasty catheter, sometimes referred to as an "over the wire" or "moveable wire" catheter, the shaft has two lumens including a guidewire lumen that extends the full length of the shaft and is adapted to moveably receive a guidewire and an inflation lumen that extends from the proximal end of a shaft to the interior of the balloon for inflation and deflation of the balloon. In use, the catheter is manipulated and advanced through the patient's arteries to place the balloon at the treatment site. More specifically, the catheter is directed to the intended treatment site by cooperative use of the guidewire which is advanced through the patient's arteries to and through the site of the arterial obstruction (the stenosis) to be treated. After the guidewire is so positioned, the catheter then is pushed along the guidewire so that it advances toward the stenosis. The catheter is advanced until the balloon, which is in a deflated condition, is inside the stenosis. The balloon then is inflated under high pressure to forcefully dilate the stenosis and enlarge the flow area through the artery.
In general, it is more difficult to advance a catheter into the more distal arteries because those arteries are very narrow and present increased resistance to an advancing catheter. The arteries also may be very tortuous, which adds further to the difficulty of advancing the catheter. Generally, when it is desired to access a distal artery, it is necessary to use a smaller diameter catheter having a relatively low profile (reduced cross section), particularly in the area of the balloon which must be passed into the stenosis. Smaller diameter catheters, however, tend to have reduced column strength and may tend to buckle in accordion-like fashion when pushed against an artery or stenosis that presents significant resistance. Also, among the difficulties sometimes presented with angioplasty catheters is that the catheter may not track along the guidewire as desired. For example, if the stiffness of the catheter relative to the guidewire is too great then the advancement of the catheter may pull the guidewire out of position. Such difficulties in trackability may be exaggerated in tortuous or narrow arteries. It would be desirable, therefore, to provide a catheter and guidewire system that reduced the tendency for the catheter to collapse longitudinally when advanced through a tight stenosis, even when the catheter is of small diameter. It also would be desirable to provide such a catheter arrangement in an over the wire configuration that displays improved trackability characteristics.
As mentioned, angioplasty catheters that are intended to be used in the smaller distal arteries must have a low profile, particularly in the balloon area when the balloon is deflated. The low profile enhances the ability of the balloon region of the catheter to pass through small diameter blood vessels and into a tight stenosis. The extent to which the diameter of the catheter can be reduced, however, is limited by a number of factors, including the number of lumens in the catheter. As described above, a common construction for an angioplasty catheter includes an elongate flexible shaft having two lumens, including a guidewire lumen and an inflation lumen. The smallest diameter coronary angioplasty catheters having such a two lumen configuration is of the order of 0.040-0.055 inches diameter.
Another type of balloon angioplasty catheter is the "fixed-wire" type of catheter in which the catheter has a single lumen and is mounted directly and permanently on the guidewire, with the guidewire passing through the single lumen. Because such a catheter requires only a single lumen, it may be made in a smaller diameter than the two lumen catheters. Such fixed wire catheters, although providing a reduced profile, have presented some difficulties in steering and manipulation of the self contained guidewire. For example, among the problems presented has been that the balloon sometimes would become wrapped about the guidewire as the guidewire was rotated and manipulated. Additionally, typical fixed wire catheters do not permit a catheter exchange to be performed without losing guidewire position in the stenosis. It would be desirable, therefore, to provide an improved low profile single lumen catheter that avoids the foregoing difficulties.